From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C2101C433F5 for ; Mon, 14 Mar 2022 12:57:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C116A6B0072; Mon, 14 Mar 2022 08:57:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B97E56B0073; Mon, 14 Mar 2022 08:57:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A11C68D0003; Mon, 14 Mar 2022 08:57:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.25]) by kanga.kvack.org (Postfix) with ESMTP id 8B6EB6B0072 for ; Mon, 14 Mar 2022 08:57:07 -0400 (EDT) Received: from smtpin07.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 2F9E924A8D for ; Mon, 14 Mar 2022 12:57:07 +0000 (UTC) X-FDA: 79242992094.07.E463F85 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf04.hostedemail.com (Postfix) with ESMTP id 8541B40034 for ; Mon, 14 Mar 2022 12:57:06 +0000 (UTC) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id CBBA6218FE; Mon, 14 Mar 2022 12:57:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1647262624; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TaLNlzXGwgt3rIVBhMb8m6A+9RFUlVGbRu4EdMRGlyg=; b=eFmcNQFmrNsywdOeFr5SEDup6JsmNK0K+YScoACNqR2qy1LHFFYhq1WsNq+LI5EPmA8/2Q bQCv7UfngnJKKpainDF0pEVNMNsKVuHf3pi0c/ifsViuOWtm9nfJR/G4o6naP5tiL4+IiB 27UYnqde9XPDx7asXLRv5oXrc/eu6lc= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id A930B13B34; Mon, 14 Mar 2022 12:57:04 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id wMNRKKA7L2KcTgAAMHmgww (envelope-from ); Mon, 14 Mar 2022 12:57:04 +0000 Date: Mon, 14 Mar 2022 13:57:03 +0100 From: Michal =?iso-8859-1?Q?Koutn=FD?= To: Shakeel Butt Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Ivan Babrou , Frank Hofmann , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Daniel Dao , stable@vger.kernel.org Subject: Re: [PATCH] memcg: sync flush only if periodic flush is delayed Message-ID: <20220314125703.GA11645@blackbody.suse.cz> References: <20220304184040.1304781-1-shakeelb@google.com> <20220311160051.GA24796@blackbody.suse.cz> <20220312190715.cx4aznnzf6zdp7wv@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220312190715.cx4aznnzf6zdp7wv@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: 8541B40034 X-Stat-Signature: n5fxqch4gnjqi7tfkt51s74yhxbjtoi5 X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=eFmcNQFm; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf04.hostedemail.com: domain of mkoutny@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mkoutny@suse.com X-Rspamd-Server: rspam02 X-HE-Tag: 1647262626-11462 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi. On Sat, Mar 12, 2022 at 07:07:15PM +0000, Shakeel Butt wrote: > So, I will focus on the error rate in this email. (OK, I'll stick to error estimate (for long-term) in this message and will send another about the current patch.) > [...] > > > The benefit this was traded for was the greater accuracy, the possible > > error is: > > - before > > - O(nr_cpus * nr_cgroups(subtree) * MEMCG_CHARGE_BATCH) (1) > > Please note that (1) is the possible error for each stat item and > without any time bound. I agree (forgot to highlight this can stuck forever). > > > - after > > O(nr_cpus * MEMCG_CHARGE_BATCH) // sync. flush > > The above is across all the stat items. Can it be used to argue about the error? E.g. nr_cpus * MEMCG_CHARGE_BATCH / nr_counters looks appealing but that's IMO too optimistic. The individual item updates are correlated so in practice a single item would see a lower error than my first relation but without delving too much into correlations the upper bound is nr_counters independent. > I don't get the reason of breaking 'cr' into individual stat item or > counter. What is the benefit? We want to keep the error rate decoupled > from the number of counters (or stat items). It's just a model, it should capture that every stat item (change) contributes to the common error estimate. (So it moves more towards the nr_cpus * MEMCG_CHARGE_BATCH / nr_counters per-item error (but here we're asking about processing time.)) [...] > My main reason behind trying NR_MEMCG_EVENTS was to reduce flush_work by > reducing nr_counters and I don't think nr_counters should have an impact > on Δt. The higher number of items is changing, the sooner they accumulate the target error, no? (Δt is not the periodic flush period, it's variable time between two sync flushes.) Michal